Power over Ethernet (PoE) is a technology for supplying low voltage current and data over a common point-to-point Ethernet network cable to locations with applications that require both mediums. In some cases, power is carried on the same conductors that carry data. In other cases, power is carried on dedicated conductors within the same cable. Applications that currently benefit from PoE technology include Voice over Internet Protocol (VoIP), Internet Protocol (IP) cameras, wireless local area networks (WLAN), Wireless Access Points (WAP), Building Automation Systems (BAS), and security and access control systems.
PoE currently has two standards: Institute of Electrical and Electronics Engineers (IEEE) 802.3af (the original PoE standard) and IEEE 802.3at (known as PoE plus), which provide, respectively, about 13 Watts and about 25.5 Watts of power to connected devices. PoE has several advantages over traditional power systems used in homes and commercial buildings. For example, PoE systems are relatively low voltage, thus eliminating the need to run expensive high voltage wiring and conduit for lighting. In addition, installation of PoE wiring can be faster than with traditional power systems because Ethernet cabling employs simple plug-in end connections.
Light emitting diode (LED) luminaires can benefit from connection to a PoE network. Recent advances have reduced the power required to operate LED luminaires to a point where network switches that are compliant with PoE standards such IEEE 802.3 at can supply the power required by the LED luminaires. In addition, proprietary specifications for PoE exist as well as new proposed standards that increase the power supplied to the PoE devices up to 90 Watts. In addition, digital Ethernet communications can be used to command the LED luminaires to dim and brighten, change color, as well as to report status such as lamp failure and energy consumption.
Track lighting is a common form of interior lighting, often used in commercial buildings. It can be found in retail spaces where the light fixtures, supported on a track, can be easily aimed toward a desired area in order to highlight or draw attention to certain aspects of displayed products. The track itself is typically a linear metal channel having one or two electrical circuits for supplying alternating current (AC) power to the multiple light fixtures (referred to as “track heads”) that are connectable at any point along the length of the track.
In some cases, it is desirable to control the brightness of one or more individual track heads. With only one or two AC electrical circuits disposed in or on the track, it can be difficult to control the brightness of the individual track heads using conventional dimmers. Often conventional dimmers are limited to controlling all of the heads on the track together and at the same intensity, since they all receive power from the same AC electrical circuit.
Recent advances in general LED light fixtures have enabled precise digital control of illumination and color of the light emitted from LED light fixtures. Digital feedback of lamp health status is also possible. Applying digital control to a single permanently fixed LED luminaire is fairly straightforward, and the use of addressable wired communications protocols such as digital addressable lighting interface (DALI) (International Electrotechnical Commission (IEC) 62386) is commonly used. It is difficult, however, to apply this wired communications protocol to commonly available individual track heads because there is currently no way of connecting the wired digital signal to each head.
Attempts have been made to communicate with individual track heads using radio frequency (RF) transmission, however it is expensive to incorporate RF transceivers into every track head. In addition, managing a large wireless network of such track heads can result in undesired interference from other RF sources in the serviced space.
Attempts have also been made to incorporate a low voltage control data bus into the AC powered track channel using separate conductors. However due to the high voltage of AC powered track lighting which may be up to 277 VAC, this may result in a dangerous mix of low voltage NEC class 2 conductors with high voltage conductors in a single-track channel. Another disadvantage of using an AC powered track lighting system in combination with LED enabled track heads is that each track head must have its own separate AC to DC converter to convert the AC electrical current into DC current that the LEDs require. As a result, each track head will lose a substantial amount of energy due to the efficiency loss during the AC to DC conversion process, thereby reducing the amount of energy that may have been saved. Also, the AC to DC conversion circuitry is costly, adding to the cost of each track head.
Energy codes regulate how much light power can be installed in a space. This is commonly referred to as Lighting Power Density (LDP) and is measured as total Watts of installed lighting, whereas a specific space in a building may not exceed the LPD specified in the energy code. Recent energy codes have required the use of expensive AC current limiters to be installed in the electrical circuit of AC powered tracks to make sure that a user cannot exceed the LPD allowed for the section of track by adding additional track heads after the building has been approved.
Using LED lamps in general lighting fixtures has the advantage of saving energy since the LED lamps themselves have a much higher efficiency than incandescent lamps. LED lamps also produce the same amount of light as incandescent lamps, while using much less energy and producing less heat. Thus, it would be desirable to provide an improved track lighting system for LED luminaires. More particularly, it would be desirable to provide a track lighting system in which the individual LED luminaires on a particular track can be independently controlled, thus enabling independent adjustment of the brightness, color, etc. of specific LED luminaires (or groups of LED luminaires) separate from the remaining LED luminaires on the track.